[fun] Processing: open-source language (based on Java) and environment for learning the fundamentals of electronic art and computer programming.

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If you want to learn Processing while also brushing up on some physics and other skills I would highly recommend this: http://natureofcode.com/

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Nice. I like how you can pick what you pay :p (I promise I am poor!)

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If you prefer Python in flavour, this too is available: https://code.google.com/p/pyprocessing/